La Niña conditions emerged in September 2025, as indicated by the expansion of below-average sea surface temperatures (SSTs) across the central and eastern equatorial Pacific Ocean [Fig. 1]. The latest weekly Niño-3.4 index value was -0.5°C, with other regions remaining at or between -0.1°C and -0.4°C [Fig. 2]. Negative subsurface temperature anomalies persisted (averaged from 180°-100°W; [Fig. 3]), with below-average temperatures prevailing from the surface to 200m depth in the eastern half of the equatorial Pacific [Fig. 4]. Over the western and east-central equatorial Pacific, low-level wind anomalies were easterly and upper-level wind anomalies were westerly. Convection continued to be enhanced over Indonesia and was suppressed near the Date Line [Fig. 5]. The equatorial Southern Oscillation index was positive. Collectively, the coupled ocean-atmosphere system reflected La Niña conditions.

The IRI multi-model predictions favor La Niña through the Northern Hemisphere winter 2025-26 [Fig. 6]. The North American Multi-Model Ensemble is also in agreement, and based on recently observed anomalies, the team favors La Niña to continue through winter. At this time, La Niña is expected to remain weak (3-month average Niño-3.4 index value at or between -0.5°C and -0.9°C). A weak La Niña would be less likely to result in conventional winter impacts, though predictable signals could still influence the forecast guidance (e.g., CPC's seasonal outlooks). In summary, La Niña conditions are present and favored to persist through December 2025 - February 2026, with a transition to ENSO-neutral likely in January-March 2026 (55% chance; [Fig. 7]).